(1) Field of the Invention
The present invention relates to a camera system having a flash device, and more particularly to a technique of controlling the flash device from a camera body.
(2) Description of the Prior Art
In a known camera system having a flash device, the flash device has a light emitter projectable from and retractable into a flash body built in the camera body. Moreover, the flash device is switchable between an operable state with the light emitter projecting from the flash body and an inoperable state with the light emitter contained in the flash body. The camera system includes an opening mechanism for switching the flash device between the two states, and a starter switch for switching between an operation prohibiting state and an operation permitting state.
In the camera system noted above, the operating mechanism for switching the flash device between the two states is controlled by the following constructions:
(I) A manually operable switch is provided with a control device for detecting the operation of this switch and actuating the above-mentioned operating mechanism. The control device includes a lock mechanism for holding the light emitter in the retracting position which is urged to the projecting position. The lock mechanism is released when the switch is turned on.
(II) A metering device is provided for detecting brightness of a photographic object. The operating mechanism is automatically operable in response to results of metering by the metering device. The flash device is switched to the operable state when the metering device provides a low luminance detection signal, and is maintained in the inoperable state at other times.
The above constructions have the following disadvantages:
The construction (I) requires the switch specially for switching the flash device. The photographer could forget to operate this switch. If its operation is forgotten when a photographic object has a low luminance level requiring flash light, a photograph with correct exposre cannot be taken at a desired shutter chance.
In the construction (II), the operating mechanism is automatically operable in response to the luminance of the object detected by the metering device. The light emitter is in the operable position whenever the luminance of the object is below a predetermined level, which is free from the problem occurring with the construction (I). With cameras in general, the release button for starting a shutter release operation often has an additional function to start the metering operation before the shutter release operation for an intensive overall operation. In this case, the flash device is switched to the operable state in response to results of metering by the metering operation. A shutter release operation for flash photography cannot be started during the time taken for this switching. Because of this time lag, a momentary shutter chance may escape.
In another known camera system with a flash device, the camera body and the flash device detachably attached to the camera body include synchronizing contacts for transmitting an emission start signal output with an operation of a synchronizing switch in the camera body to the flash device, and charge controlling contacts for transmitting a charge control signal to a capacitor in the flash device for accumulating emission energy. Not only start of emission of the flash device but energy accumulation for the emission is controlled from the camera body.
In this type of camera, the synchronizing contacts and charge controlling contacts comprise separate contacts in the camera body and flash device, respectively, since these contacts transmit the different signals.
The separate synchronizing contacts and charge controlling contacts result in an increase in the number of parts of such a camera. The camera body generally includes a hot shoe while the flash device includes a foot, for attaching the flash device to the camera body. In this case, the separate contacts as noted above result in an increase in the number of contacts arranged in limited regions of the hot shoe and foot. Ths gives rise to the problem of spatial restriction to the arrangement of the contacts and the like.
In recent years particularly, various operations of the flash device are often controlled by a control device in the camera body to achieve an intensive overall operation. Such controls include not only the emission of and energy accumulation in the flash device, but control of an amount of light emission from the flash device based on flash light measured by the camera body, and control of an illuminating angle of the flash device in accordance with the focal length of an objective lens attached to the camera body. In this case, the above-mentioned problem is striking since the camera body and flash device must include contacts for transmitting various signals.
In a further known camera system with a flash device, the flash device includes a control circuit for controlling an overall operation of the flash device, and a boosting and flashing circuit. Depending on the type of flash device, these control circuit and the boosting and flashing circuit are operable with a voltage above ground level or with a voltage below ground level.
Assume here that a flash device having a control circuit and a boosting and flashing circuit operable with a voltage below ground level is attached to a camera body designed for attaching a flash device having a control circuit and a boosting and flashing circuit operable with a voltage above ground level. In this case, a voltage reverse to normal will act between the synchronizing terminal and the grounding terminal of the camera body, which results in malfunctioning of the camera.
A known measure taken to avoid this reverse voltage is connection of the synchronizing terminal and the grounding terminal through a diode. However, the camera body and the flash unit are often sold as a system, with the two items designed in matching relationship. In this case, the construction for preventing the reverse voltage would increase the cost of the camera body.